Modern aircraft incorporate horizontal stabilizers or canards (tails) to provide trim for level flight and control of roll, yaw, and pitch. These tails normally are designed to pivot on spindles to provide incidence deflection angles to enable effective control at supersonic speeds, where conventional "flapped" horizontal tails and elevators are ineffective due to shock waves. However, at subsonic maneuvering speeds these spindled tails generate less lifting coefficient than flapped tails, thus larger tails are required. At subsonic speeds large tails create more skin friction drag and supersonic speeds large tails create additional wave drag. The designer must balance these two constraints, producing an aircraft that is neither optimized for supersonic speeds or slower speeds.
Thus there exists a need for a smaller tail that can produce large lifting forces/moments at low speeds (high angles of attack) and still pivots to create effective control at supersonic speeds in the presence of shock waves.